Public bug reported:
Version:
chromium 87.0.4280.66 1411
Steps to reproduce:
1. Have Chromium snap, with raw-usb plug connected.
2. sudo modprobe usbmon.
3. Open Chromium and try to use a webpage that has webusb.
Result:
Chromium cannot see any USB devices on the system, regardless of whether
it has raw-usb or not.
The following errors are printed on dmesg:
```
[3701471.283584] audit: type=1400 audit(1606101844.664:6015): apparmor="DENIED"
operation="open" profile="snap.chromium.chromium" name="/run/udev/data/c508:4"
pid=3120526 comm="ThreadPoolForeg" requested_mask="r" denied_mask="r"
fsuid=1000 ouid=0
[3701471.283636] audit: type=1400 audit(1606101844.664:6016): apparmor="DENIED"
operation="open" profile="snap.chromium.chromium" name="/run/udev/data/c508:2"
pid=3120526 comm="ThreadPoolForeg" requested_mask="r" denied_mask="r"
fsuid=1000 ouid=0
[3701471.283700] audit: type=1400 audit(1606101844.664:6017): apparmor="DENIED"
operation="open" profile="snap.chromium.chromium" name="/run/udev/data/c508:0"
pid=3120526 comm="ThreadPoolForeg" requested_mask="r" denied_mask="r"
fsuid=1000 ouid=0
[3701471.283786] audit: type=1400 audit(1606101844.664:6018): apparmor="DENIED"
operation="open" profile="snap.chromium.chromium" name="/run/udev/data/c508:7"
pid=3120526 comm="ThreadPoolForeg" requested_mask="r" denied_mask="r"
fsuid=1000 ouid=0
[3701471.283869] audit: type=1400 audit(1606101844.664:6019): apparmor="DENIED"
operation="open" profile="snap.chromium.chromium" name="/run/udev/data/c508:5"
pid=3120526 comm="ThreadPoolForeg" requested_mask="r" denied_mask="r"
fsuid=1000 ouid=0
[3701471.283982] audit: type=1400 audit(1606101844.664:6020): apparmor="DENIED"
operation="open" profile="snap.chromium.chromium" name="/run/udev/data/c508:3"
pid=3120526 comm="ThreadPoolForeg" requested_mask="r" denied_mask="r"
fsuid=1000 ouid=0
```
Chromium will then print this on stderr:
```
[3121487:3121626:1123/032552.888385:ERROR:udev_watcher.cc(97)] Failed to begin
udev enumeration.
```
Why this happens:
Chromium enumerates USB devices by querying udev. Specifically by using
udev_enumerate_scan_devices. When usbmon module is loaded, some new
device nodes are created for the monitor endpoints. They are only
readable by root. When Chromium scans for normal USB devices, it finds
the monitors and tries to probe them. Apparmor blocks it, which causes
udev_enumerate_scan_devices to fail.
Impact:
There is no way for the user to know this error has occurred unless they
happen to be watching dmesg or the stderr of Chromium (which requires
they ran it from a terminal). Unless they check both of these places and
realize that the error messages are connected, Chromium will just appear
to behave as if there are no USB devices connected to the system at all.
If the user does realize that usbmon is causing a problem, they must
restart Chromium after unloading it, because it will not retry if
enumeration ever fails.
** Affects: chromium-browser (Ubuntu)
Importance: Undecided
Status: New
** Description changed:
Version:
chromium 87.0.4280.66 1411
-
Steps to reproduce:
1. Have Chromium snap, with raw-usb plug connected.
2. sudo modprobe usbmon.
3. Open Chromium and try to use a webpage that has webusb.
Result:
Chromium cannot see any USB devices on the system, regardless of whether
it has raw-usb or not.
The following errors are printed on dmesg:
```
[3701471.283584] audit: type=1400 audit(1606101844.664:6015):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:4" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283636] audit: type=1400 audit(1606101844.664:6016):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:2" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283700] audit: type=1400 audit(1606101844.664:6017):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:0" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283786] audit: type=1400 audit(1606101844.664:6018):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:7" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283869] audit: type=1400 audit(1606101844.664:6019):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:5" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
[3701471.283982] audit: type=1400 audit(1606101844.664:6020):
apparmor="DENIED" operation="open" profile="snap.chromium.chromium"
name="/run/udev/data/c508:3" pid=3120526 comm="ThreadPoolForeg"
requested_mask="r" denied_mask="r" fsuid=1000 ouid=0
```
Chromium will then print this on stderr:
- And the following error is printed on stderr of Chromium:
+
```
[3121487:3121626:1123/032552.888385:ERROR:udev_watcher.cc(97)] Failed to
begin udev enumeration.
```
-
Why this happens:
Chromium enumerates USB devices by querying udev. Specifically by using
udev_enumerate_scan_devices. When usbmon module is loaded, some new
device nodes are created for the monitor endpoints. They are only
readable by root. When Chromium scans for normal USB devices, it finds
the monitors and tries to probe them. Apparmor blocks it, which causes
udev_enumerate_scan_devices to fail.
Impact:
There is no way for the user to know this error has occurred unless they
happen to be watching dmesg or the stderr of Chromium (which requires
they ran it from a terminal). Unless they check both of these places and
realize that the error messages are connected, Chromium will just appear
to behave as if there are no USB devices connected to the system at all.
If the user does realize that usbmon is causing a problem, they must
restart Chromium after unloading it, because it will not retry if
enumeration ever fails.
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/1905458
Title:
[snap] Chromium USB enumeration fails with usbmon module is loaded
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/chromium-browser/+bug/1905458/+subscriptions
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